Saccharomyces cerevisiae Supplementation Enhances Growth and Immune Response in Nile Tilapia During Winter Stress

The purpose of this study was to evaluate the effects of baker's yeast (Saccharomyces cerevisiae) supplementation on growth, immune-related gene expression, and disease resistance in Nile tilapia (Oreochromis niloticus) during the winter season. Fish (an average 5.17 ± 0.33 g) were fed diets containing four different S. cerevisiae concentrations: 0 g/kg (control; T1), 5 g/kg (T2), 10 g/kg (T3), and 20 g/kg (T4) for 90 days. The results showed that weight gain (WG) and specific growth rate (SGR) were significantly higher in fish-fed the T4 diet compared to the control group (p < 0.05). Additionally, fish-fed the T4 diet showed lower carcass yields but higher fillet yields, along with increased amylase and protease activities (p < 0.05). Significant increases (p < 0.05) in serum lysozyme activity were found in fish-fed the T4 supplemented diet, and elevated myeloperoxidase (MPO) levels were observed in fish-fed the T3 diet. Moreover, upregulation of il-8 transcription in the liver was noted in fish feeding S. cerevisiae (T2-T4) compared to the control group. In a challenge test against Streptococcus agalactiae, survival rates (SRs) were significantly higher in fish-fed the T4 diet compared to the control group (p < 0.05). Interestingly, the lowest bacterial counts were recorded in the T3 group (p < 0.05). These findings suggest that dietary supplementation with S. cerevisiae at 10-20 g/kg enhances growth performance, digestive enzyme activity, immune responses, and disease resistance in Nile tilapia during winter conditions.